Ballast apparatus using leakage reactance of split primary winding



Dec. 24, 1968 Filed March 3. 1967 BALLAST APPARAT- OF SPLIT PRIMARYWINDING 5 Sheets-Sheet 1 m I l {RI 5 I13 c .rZO

s l2 L3 R2 W i F IG.1 P PRIOR ART L3 I FIG.'IA PRIOR ART a) 27 2' P2 EFZ2s I23 INVENTOR IMRICH M. MILLER BY rofl ATTORNEYS Dec. 24, 1968 M.MILLER BALLAST APPARATUS USING LEAKAGE RE ACTANCE OF SPLIT PRIMARYWINDING 5 Sheets-Sheet 2 Filed March 5, 1967 HJVEMTOR HQRICH M. NHLLERATTORN EYS Dec. '24, 1968 BALLAST APPARATUS USING LEAKAGE REACTANCEFiled Match 3. 1967 I. M. MILLER OF SPLIT PRIMARY WINDING 5 Sheets-Sheet5 A s RI: FIG 4 :F R |4 2 'T P.

,l6 1 27" 2| 2 Q 2% lo 8 F ML n I FIG 5 S r 'jc 20 P|-1 L4 7 26\NF'T Ci]1 L l4 L I I0 P2 w 2 0% 27/ r2l 2a- F3 \n INVENTOR IMRICH M. MILLERATTORNEYS Dec. 24, 1968 M. MILLER BALLAST APPARATUS USING LEAKAGE REACTANCE OF SPLIT PRIMARY WINDING 5 Sheets-Sheet 4 Filed March 5, 1967 FIG.6

INVENTOR IMRICH M. MILLER ATTORNEYS 3,418,527 NOE Dec. 24, 1968 M.MILLER PPARATUS USING LEAKAGE REACTA OF SPLIT PRIMARY WINDING BALLAST A5 Sheets-Sheet 5 Filed March 3, 1967 FIG. 8

INVENTOR IMRICH M MILLER ATTORNEYS United States Patent 3,418,527BALLAST APPARATUS USING LEAKAGE RE- ACTANCE 0F SPLIT PRIMARY WINDINGImrich M. Miller, Passaic, N.J., assignor to Universal ManufacturingCorporation, Paterson, N.J., a corporation of New Jersey Filed Mar. 3,1967, Ser. No. 620,334 12 Claims. (Cl. 315-244) ABSTRACT OF THEDISCLOSURE Ballast transformers for fluorescent lamps in which a circuitis used in shunt with a secondary winding of the transformer to resonatewith it and increase the open circuit starting voltage. The primarywinding of the transformer is split and the shunt circuit is dischargedthrough the split primary to damp the discharge.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to ballast apparatus for starting and operating gaseousdischarge lamps and more particularly to an improved ballast apparatusemploying high reactance transformers with a shunting capacitorconnected in parallel circuit relation with the transformer secondary toincrease the ballast output.

Description of the prior art High reactance ballast transformers arecommonly used to provide the Voltages required for starting andoperating one or more fluorescent lamps. Such transformers usuallycomprise a shell-type core of magnetic saturable material with anelongated center leg on which the primary and one or more secondarywindings are located in an inductive coupled relationship. A capacitoralso is usually connected in series circuit with a secondary winding andthe running circuit of the lamp or lamps to provide a net capacitivereactance (lead current) in the lamp circuit during normal runningoperation.

In high reactance transformers of the type described above, saturationof the magnetic core is relied upon to provide current limiting andoutput voltage regulation during operation of the lamps. In general, thetransformer is designed to provide a desired value of open circuitvoltage for lamp starting. The open circuit starting voltage is usuallysubstantially higher than the running voltage. However, the high opencircuit voltage is preferably produced with a minimum number ofsecondary winding turns. The secondary turns are minimized in order tomaintain the transformer leakage reactance at the lowest possible valueconsistent with good performance. However, suflicient turns are used toprovide good regulation of the secondary current.

As is known, the open circuit RMS (root mean square) voltage requiredfor starting a particular fluorescent lamp, or lamps, varies with thelamp length. Also, for any given lamp length a peak voltage requirementis imposed for reliable starting which peak voltage in large measuredepends upon the lowest temperature of the environment in which the lampis to be started and operated. Thus, even though the secondary turns aredesirably held to a minimum the transformer still is usually required toproduce a high output voltage for starting, which voltage must be higherfor longer length lamps.

To produce the high starting voltages needed for longer length lampssome ballasts utilize a resonant circuit formed by a series connectedinductor and a capacitor. At least the capacitor of the resonant circuitis connected in shunt with a lead secondary winding of a high reactanceballast transformer. The shunt circuit provides one or more preselectedharmonic components in the secondary winding which are combined with thetransformed line voltage to produce a higher voltage to aid in starting.In effeet, the shunt circuit produces a higher RMS open circuit voltagefor a given number of secondary turns, resulting in a reduction in thetotal number of secondary turns needed for a given starting voltagerequirement, and also causes a decrease in leakage reactance. The lattergives rise to an increase in the coupling between the transformerprimary and secondary windings.

While the shunt capacitor in the resonant circuit of the type of ballastdescribed above is effective in increasing the lamp starting voltage, itintroduces at least one major problem in that it makes the currentflowing through the lamps have sharp spikes. These sharp spikes areunwanted since, in some cases, when they reach sufficient amplitude theyseriously harm the lamp. The magnitude of these undesirable spikesincrease with lamps operating in a cold environment, e.g. 20 C. andbelow, because of changes in the impedance of the lamps which are in thecapacitors discharge circuit.

Several circuit arrangements have been proposed for eliminating thespikes when using the shunt capacitor as part of a resonant circuit inthe ballast secondary. One such arrangement is described in Hume Patent3,225,255. In that patent, a reactive impedance is connected in serieswith the shunt capacitor to form the shunt circuit across the leadsecondary winding. The alleged purpose of this impedance is to controlthe discharge of the shunt capacitor in each half-cycle of lampoperation and thereby damp the spikes. While this arrangement isoperative in most respects, it is undesirable since an additionalreactor (impedance), usually an inductor, must be utilized.

In another type of transformer using a harmonic producing shunt circuitcapacitor, a split primary winding is also used wherein only a portionof the primary winding is coupled with the secondary winding. Hence, theshunting circuit is connected across both the secondary winding and oneof the split primary windings. This expedient further increases thecoupling factor of the ballast transformer thereby further reducing thenumber of secondary turns needed for a given RMS voltage requirementwhile not reducing the leakage reactance. However, an inductor stillmust be used in series with the capacitor to damp the spikes.

SUMMARY OF THE INVENTION It is the purpose of the present invention toprovide a high reactance type ballast transformer for fluorescent lampsusing a capacitor in shunt with the secondary Winding in which noadditional reactor is required to damp the voltage spikes produced bythe capacitor during operation at normal temperatures, i.e. above about20 C. Also, according to the present invention, when the ballast is tobe used in a low temperature environment a reactor of substantiallysmaller size is required as compared to prior art ballasts. In bothcases, a substantial savings in material and other manufacturing costsis effected.

In accordance with the preferred embodiment of the invention, atransformer with a split primary winding is used in which the dischargepath of the secondary winding shunting capacitor is through the entireprimary winding. Since the split primary winding is provided with itsown leakage reactance, it damps the discharge of the shunting capacitor,thereby smoothing out the waveform of the current flowing through thelamp or lamps. In another embodiment of the invention, which isparticularly useful in low temperature applications -where a higherstarting voltage is needed, a reactor is used in series with theshunting capacitor. Here, the discharge path of the shunting capacitoris still through the entire split primary winding, so that the size ofthe reactor is reduced from that which would normally be required inprior art ballasts with a consequent saving in cost. In both embodimentsof the invention the main capacitor usually provided in the operatinglead circuit can be made a part of or used externally to the shuntingcircuit.

It is therefore an object of the present invention to provide animproved ballast apparatus for starting and operating one or morefluorescent lamps in an improved series lead circuit arrangement.

Another object is to provide an improved ballast apparatus using ashunting capacitor across the secondary winding to form a tuned harmonicproducing circuit, with the discharge of the capacitor through lampsbeing damped by the split transfomer primary winding.

A further object is to provide a ballast transformer having a splitprimary winding and a capacitor in shunt with the secondary winding, thedischarge path of the capacitor being through the entire split primarywinding.

An additional object is to provide a ballast transformer with a splitprimary winding and a series connected reactor and capacitor in shuntwith the secondary winding, the discharge path of the series connectedcomponents being through the entire split primary winding.

Other objects and advantages of the present invention will become moreapparent upon reference to the following specifications and annexeddrawings, in which:

FIGS. 1 and 1A are schematic diagrams of prior art high leakagereactance ballast transformers with a capacitor shunting the secondarywinding;

FIG. 2 is a schematic diagram of a ballast transformer in accordancewith the present invention;

FIG. 3 is a schematic diagram of a ballast transformer constructed inaccordance with another embodiment of the invention;

FIGS. 4 and 5 are schematic diagrams showing variations of theembodiments of FIGS. 2 and 3, respectively;

FIG. 6 is a' schematic diagram of a ballast which is a modification ofthe ballasts of FIGS. 2 and 4;

FIG. 7 is a schematic diagram of a ballast which is a modification ofthe ballasts of FIGS. 3 and 5; and

FIG. 8 is a plan view of one form of ballast constructed in accordancewith the present invention.

FIG. 1 shows a prior art type ballast transformer using a tuned circuitacross the secondary winding to produce the harmonics for higherstarting voltages. Here, a con tinuous wound primary winding P of thetransformer has its ends connected by a pair of leads 10 and .11 to asuitable source of alternating current (not shown). The lower end of thesecondary winding S is autotransfonmer connected to the upper end of theprimary at junciton 12. The primary P and secondary S are wound on acore shown schematically at 13 and a flux leakage path 14 is providedbetween windings P and S. In one common configuration the transformer isof the shell type whose laminations have a central leg surrounded by anouter frame, all of which is made of magnetic saturable material. Thecenter leg corresponds to element 13 of" FIG. 1. The flux leakage path14 may be formed, if desired, by non-magnetic material, such as an airgap between the primary and secondary. It also can be formed of magneticmaterial such as by projecting shunt legs formed on the transformerlaminations or by shunts inserted between the primary second windings.

Secondary winding S supplies a pair of fluorescent lamps and 21 ofconventional construction and they are preferably positioned in amounting fixture (not shown) preferably in close proximity to a groundedconductive fixture member or plate 23, so that the lamps are disposed incapacitive relationship therewith. The filamentcathodes 25 and 26 oflamp 20 and the filament-cathodes 27 and 28 of lamp 21 are provided withcurrent during operation by a plurality of filament windings F1, F2 andF3. Cathodes 25 and 26 are supplied with current by leads connected towindings F11 and F2, while cathodes 27 :and 28 are supplied by windingsF2 and F3, Wipdin gs F1 and F2 are preferably tightly coupled to theprimary winding P and may, if desired, be wound directly over theprimary while winding F3 is an extension of the primary winding.

The upper end of secondary winding S is connected by a capacitor C1 tothe electrode 25 at one end of lamp 20, and electrode 28 at the lowerend of the series connected lamp 21 is connected by one of the leads offilament winding F3 to the lower end of primary winding P. The other twoelectrodes 26 and 27 of the two lamps are connected together by thefixture wiring .Thus, the full transformer voltage of 'autotransformerconnected windings P and S is applied across the series connected lamps20 and 21. Capacitor C1 provides a net capacitive reactance in therunning lamp circuit, i.e. during operation after starting.

A starting capacitor C2 is connected across lamp 21 so that thetransformers open circuit starting voltage is initially applied onlyacross lamp 21. Resistors R1 and R2 are connected in parallel with therespective capacitors C1 and C2 to discharge these capacitors when theballast is inoperative.

In the prior art ballast of FIG. 1, the secondary winding S is shuntedby the series connected circuit of R1 and C1 in parallel, a capacitorC3, and a reactive impedance illustratively shown as an inductor L3. Ingeneral, the shunting capacitor C3 provides sufiicient capacitivereactance in the secondary circuit to resonate with the other seriescircuit elements at a preselected harmonic frequency and produce aharmonic voltage component which is added to the transformed secondaryvoltage of 60 HZ to produce an overall higher voltage. The harmonicfrequency selected may be, for example, the seventh harmonic of the linevoltage, 420 Hz. The purpose of the inductance L3, for example asdescribed in Hume Patent 3,225,255, is to control the discharge ofcapacitor C3 in each half cycle of lamp operation so that unnecessarilylarge current spikes which might damage the lamp will not be produced bythe shunting capacitor C3.

FIG. 1A shows another prior art circuit for producing the harmonicvoltage in which the same reference characters and numbers are used forthe same parts. Here, the primary winding is split into two sections P1and P2 with a high leakage reactance 16, similar to leakage reactance14, located between the two sections. In this circuit, the runningcapacitor C1 and its parallel connected discharge resistor R1 areconnected outside of the resonant harmonic producing circuit formed bythe series connected capacitor and inductor, C3 and L3. The latter twocomponents are connected from the upper end of the secondary winding Sto the junction point 17 of the split primary sections. As in thecircuit of FIG. 1, the reactor L3 serves to damp the discharge ofcapicitor C3. The lower primary section P2 also provides some dampingaction here but the leakage reactance 16 is not effectively in thedamping circuit. The latter is true because junction 17 is effectivelyacross both sides of the shunt 16, i.e., no current from C3 and L3passes through both P1 and P2 to be affected by leakage reactance 16'.

While the circuits of FIG. 1 and 1A are operative, they have at leastone major disadvantage in that they require the extra inductor (choke)L3 to dampen the discharge of the shunting capacitor C3. Such anarrangement adds to the cost of the ballast due to the requirement ofthe extra component L3 and the extra assembly steps and parts needed toput it in the circuit.

FIG. 2 is a schematic diagram of a ballast apparatus made in accordancewith the present invention. Similar reference numerals are used whereapplicable for the same components shown in FIGS. 1 and 1A. In theballast of FIG. 2 the primary winding is split into two portions P1 andP2 which are separated by the leakage reactance 16. Thelatter may beformed either by an air gap, shunt legs on the laminations, or by shuntsinserted. between the two sections of the primary winding, the same asthe leakage reactance 14. The secondary winding S is shunted only by acapacitor C4 connected to the lower end 18 of the secondary, There is noimpedance in series with this capacitor in the portion of the circuitshunting secondary winding S. The .remaining components of the ballastapparatus of FIG. 2 are the same as those shown in FIG. 1A and theyperform the same function.

The operation of the ballast of FIG. 2 is similar to that of FIG. 1A.Here, capacitor C4 is tuned with the secondary winding S to be resonantat a selected harmonic of the line frequency. This produces theincreased voltage for application to the lamps. In this circuit,however, rather than controlling the discharge of capacitor C4 by aseperate reactance member such as L3 in series with the shunt capacitor,the discharge of capacitor C4 is damped by the high leakage reactance 16between the split primary windings P1 and P2. The entire primary windingP1 and P2 from the connection point of the capacitor C4 and thesecondary S down to the wire 10, which is actually the common side ofthe transformer, forms the discharge path for capacitor C4. Since thecapacitor discharge current flows through both P1 and P2, the highleakage reactance 16 is in the capacitors discharge circuit. Leakagereactance 16 substantially damps the discharge of the capacitor C4 oneach half-cycle to smooth out the waveform, so that no current spikesappear which might damage the lamps 20 and 21.

FIG. 3 shows another embodiment of the invention which is similar to theballast of FIGURE 2. Here, the split primary winding P1 and P2 isutilized, and P1 is tightly coupled (for example, wound over) to S.Leakage reactance 14 is common between both P2 and S, and P1 and P2.This reduces the total leakage reactance in transformer and increasesits open circuit output voltage. In this ballast an inductor L4 isinserted in series with the shunting capacitor C4. Capacitor C4,inductor L4 and S are tuned to resonate at the desired harmonicfrequency. The discharge path of C4 is through L4, P1, leakage reactance14 and P2.-

The ballast of FIG. 3 finds particular use in low temperatureenvironments since it is capable of producing a somewhat higher startingvoltage and operating voltage than the ballast of FIG. 2. It should benoted however that the inductor L4 used in the secondary shuntingcircuit can be made considerably smaller than the inductor L3 in theshunting circuit of the ballast of FIGS. 1 or 1A. This again is due tothe fact that inductor L4 itself is not itself used to damp out thedischarge of the shunting capacitor C4 since this is in large measureaccomplished by the high leakage reactance 14 between the split primarywindings P1 and P2.

FIGS. 4 and 5 show circuits similar to FIGS. 2 and 3, respectively. Theonly difference is that in each case the running capacitor C1 has beenmoved to be in series with shunt resonating capacitor C4 acrosssecondary S. C1 now becomes a part of the resonant circuit. Operation ofthese two circuits is otherwise the same as in FIGS. 2 and 3.

FIG. 6 shows a further modification of the ballasts of either of FIGS. 2or 4. Here, P1 is tightly coupled to S, as in the ballasts of FIGS. 3and 5, and leakage reactance 14 is common to both P2 and S, and P1 andP2. Leakage reactance 14 is in the discharge circuit of capacitor C4 andserves to damp the discharge. As in FIGS. 2 and 4, there is no otherinductor, such as L4, in the discharge circuit. While the ballast ofFIG. 6 has the running capacitor outside of the resonant loop of C4 andS, it can be placed inside.

FIG. 7 shows a further modification of the ballasts of either of FIGS. 3or 5. Here, P1 and P2 are split and separated by the leakage reactance16. A separate inductor L4 is used to improve the low temperaturecharacteristics of the ballast, with leakage reactance 16 stillproviding a large portion of the damping action. While C1 is shownoutside of the resonant circuit, it can be placed inside.

FIG. 8 shows a plan view of a typical ballast transformer made inaccordance with the invention. The transformer has a shell type coreformed by a T lamination member 50 with a center leg 52 and two Llamination members 54 whose short legs abut the side of the long leg ofthe T member adjacent its end. A stack of these laminations are used andthe slots 55 and 56 perform their usual function of providing highreluctance areas on the center leg. The primary winding P1 is placed onthe long leg '52 separated from the second primary winding P2 and thesecondary winding S by the magnetic shunts 60 which form the leakagereactance 14. As shown, S is wound over P2 so that the magnetic shunts60 are common to both P2 and S.

The ballast circuits of the subject invention also can be used withshunting capacitors (C which in'herently possess an amount ofinductance. It is known that capacitors can be built with a considerableamount of inherent inductance by suitably constructing their electrodesan'd/ or connecting tabs. Thus, such capacitors can be used to eitherentirely eliminate the need for the separate shunting inductor L or toreduce its size even in low temperature applications of the ballasts ofthe subject invention where such additional inductance is sometimesrequired.

What is claimed is:

1. A ballast apparatus for one or more fluorescent lamps comprising ahigh reactance transformer with a primary winding and a secondarywinding inductively coupled on a magnetic core to produce a voltagetransfer therebetween when voltage is applied to the primary winding,said primary winding being divided into two sections, leakage reactancemeans between said two sections, shunting circuit means connected acrosssaid secondary winding in parallel circuit relation to increase thestarting voltage of the transfer, and means connecting said shuntingcircuit to said primary winding to provide a discharge path thereforthrough both sections of the primary winding and the leakage reactancemeans.

2. Ballast apparatus as set forth in claim 1 wherein said shuntingcircuit means comprises a capacitor.

3. Ballast apparatus as set forth in claim 1 wherein said shuntingcircuit means comprises a capacitor and an inductor connected in series.

4. Ballast apparatus as set forth in claim 1 wherein said shuntingcircuit means is resonant with said secondary winding at a selectedharmonic of the frequency of the voltage applied to the primary winding.

5. Ballast apparatus as set forth in claim 4 wherein said shuntingcircuit means is a capacitor.

'6. Ballast apparatus as set forth in claim 4 wherein said shuntingcircuit means comprises a capacitor and an inductor connected in series.

7. Ballast apparatus as set forth in claim 1 wherein one of saidsections of said primary winding is tightly coupled to the secondarywinding.

8. Ballast apparatus as set forth in claim 7 wherein said one section ofsaid primary winding is wound over at least a portion of said secondarywinding.

9. Ballast apparatus'as in claim 1 further comprising a capacitorconnected to one of the output leads of the secondary winding and in thelamp running circuit, said capacitor being outside of the parallelcircuit formed by the secondary winding and the shunting circuit means.

10. Ballast apparatus as in claim 1 further comprising a capacitorconnected to one of the output leads of the secondary winding and in thelamp running circuit said capacitor connected in series with saidshunting circuit means to form part of the circuit in parallel 'withsaid secondary winding.

11. Ballast apparatus as in claim 1 further comprising a separateleakage reactance means between one of said sections of said primarywinding and said secondary winding.

12. Ballast apparatus as in claim 1 wherein said leakage reactance meansis also between one of said sections of said primary winding and saidsecondary winding.

(References on following page) 7 References Cited UNITED STATES PATENTSJAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

US. Cl. X.R.

